1. Field of the Invention
The present invention relates to an electron emission device and an electron emission display device using the same.
2. Description of the Related Art
In field electron emission display apparatuses, a Field Emission Display (FED) is known as a planar emission display device equipped with an array of cold-cathode electron emission source which does not require cathode heating. The emission principle of, for example, an FED using Spindt-type cold cathodes of minute protrusions is as follows: Its emission principle is like a Cathode Ray Tube (CRT), although this FED has a cathode array of Spindt-type protrusions which is different from that of CRT. In the FED, electrons are drawn into a vacuum space by means of each gate electrode spaced apart from the Spindt-type cathode, and the electrons are made to impinge upon the fluorescent substance that is coated on a transparent anode, thereby causing light emission.
This FED, however, has a problem of low production yield because the manufacture of the minute Spindt-type emitter arrays as a cold cathode is complex and involves many processes.
There also exists an electron emission device with a metal-insulator-metal (MIM) structure as a planar electron emission source. The electron emission device with the MIM structure comprises an Al underlayer as a base electrode, an Al2O3 insulator layer with about 10 nm thickness, and an Au overlayer, as a top electrode with about 10 nm thickness which are formed in order on the substrate. In the case that this MIM device is placed under an opposing electrode in a vacuum, when a voltage is applied between the Al underlayer and the Au overlayer and, at the same time, an acceleration voltage is applied to the opposing electrode, then some of electrons emit out of the Au overlayer and reach the opposing electrode. Even the electron emission device with the MIM structure does not yet provide a sufficient amount of emitted electrons.
To improve these disadvantages of emission of the MIM device, it is conventionally considered that there is a necessity to make the Al2O3 insulator layer thinner by about several nanometers and make the Al2O3 insulator layer with a uniform quality so that the interface between the Al2O3 insulator layer and the Au overlayer is more uniform.
To provide a thinner and more uniform insulator layer, for example, an attempt has been made to control the anodized current by using an anodization method thereby to improve the electron emission characteristics, as in the invention described in Japanese Patent Application kokai No. Hei 7-65710.
However, even an electron emission device with the MIM structure which is manufactured by this anodization method ensures an emission current of about 1xc3x9710xe2x88x925 A/cm2 and an electron emission efficiency of about 1xc3x9710xe2x88x923.
Accordingly, it is an object of the present invention to provide an electron emission device with a high electron emission efficiency capable of stably emitting electrons with a low applied voltage thereto and an electron emission display apparatus using the same.
In consideration to a universal application of this electron emission device, the usage of silicon (Si) for an electron-supply layer in the electron emission device is effective to improve the stability of the device and also the use of an amorphous silicon (a-Si) layer deposited by a sputtering method is effective in a high productivity and therefore is very useful. However there is a problem that the property of the a-Si layer is apt to deteriorate due to a heat treatment thereto, because of existence of many dangling bonds e.g., about 1020/cm3 in the layer. Since the heat treatment is necessary for vacuum-packaging of the device, the existence of many dangling bonds in the amorphous silicon layer is one of obstacles to a practical use of the electron emission device display. Accordingly, it is another object of the present invention to provide an electron emission device with a high stability at a high temperature and an electron emission display apparatus using the same.
In order to overcome the foregoing and other problems, the object of the invention are realized by an electron emission device in accordance with embodiments of this invention, wherein the device according to the invention comprises:
an electron-supply layer made of metal or semiconductor;
an insulator layer formed on the electron-supply layer; and
a thin-film metal electrode formed on the insulator layer and facing a vacuum space,
characterized in that said insulator layer has a film thickness of 50 nm or greater, and said electron-supply layer is made of a silicon wafer, whereby the electron emission device emits electrons when an electric field is applied between the electron-supply layer and the thin-film metal.
Moreover a display device using an electron emission device according to the invention comprises:
a pair of first and second substrates facing each other with a vacuum space in between;
a plurality of electron emission devices provided on the first substrate;
a collector electrode provided in the second substrate; and
a fluorescent layer formed on the collector electrode,
each of the electron emission devices comprising an electron-supply layer of metal or semiconductor; an insulator layer formed on the electron-supply layer; and a thin-film metal electrode formed on the insulator layer and facing a vacuum space, wherein said insulator layer has a film thickness of 50 nm or greater, and said electron-supply layer is made of a silicon wafer.
According to the electron emission device of the invention with the above structure, dangling bonds decrease in the electron-supply layer so that the thermal stability of the device is improved, and through-bores are not likely to be produced in the insulator layer because of its relatively thick thickness and then the production yield is improved.
The electron emission device of the invention is a planar or spot-like electron emission diode and can be adapted to high speed devices such as a source of a pixel vacuum tube or bulb, an electron emission source of a scanning or transmission electron microscope, a vacuum-micro electronics device and the like. In addition, this electron emission device can serve as a minute microwave tube or a diode which emits electromagnetic waves with millimeter or sub-millimeter wavelength, and also can serve as a high speed switching device.